Non-volatile memory device and manufacturing method and operating method thereof

ABSTRACT

A non-volatile memory device having a substrate, an n type well, a p type well, a control gate, a composite dielectric layer, a source region and a drain region is provided. A trench is formed in the substrate. The n type well is formed in the substrate. The p type well is formed in the substrate above the n type well. The junction of p type well and the n type well is higher than the bottom of the trench. The control gate which protruding the surface of substrate is formed on the sidewalls of the trench. The composite dielectric layer is formed between the control gate and the substrate. The composite dielectric layer includes a charge-trapping layer. The source region and the drain region are formed in the substrate of the bottom of the trench respectively next to the sides of the control gate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of, and claims the prioritybenefit of, U.S. application Ser. No. 11/158,412 filed on Jun. 21, 2005now U.S. Pat. No. 7,154,142, which claims the priority benefit of Taiwanapplication serial no. 94100019, filed on Jan. 3, 2005. All disclosureof the Taiwan application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device. Moreparticularly, the present invention relates to a non-volatile memory(NVM) device and a manufacturing method and an operating method thereof.

2. Description of Related Art

Electrically erasable programmable read only memory (EEPROM) is a typeof non-volatile memory that allows multiple data reading, writing anderasing operations. In addition, the stored data will be retained evenafter power to the device is removed. With these advantages, it has beenbroadly applied in personal computer and electronic equipment.

A typical flash memory device has a floating gate and a control gatefabricated using doped polysilicon, and the control gate is disposeddirectly above the floating gate. Further, the floating gate is isolatedfrom the control gate with a dielectric layer, while the floating gateis isolated from the substrate with a tunnel oxide layer. With thecontrol gate, the floating gate, the dielectric layer and the tunneloxide layer, a stacked gate flash memory cell is provided.

FIG. 1 is a schematic cross-sectional view of a portion of aconventional stacked gate flash memory cell structure (refer to U.S.Pat. No. 6,214,668). As shown in FIG. 1, the conventional stacked gateflash memory cell structure includes a p-type substrate 100, a deepn-well region 102, a p-type pocket doped region 104, a stacked gatestructure 106, a source region 108, a drain region 110, a spacer 112, aninterlayer dielectric layer 114, a conductive plug 116 and a conductiveline 118 (bit line). The stacked gate structure 106 is constituted witha tunnel oxide layer 120, a floating gate 122, a gate dielectric layer124, a control gate 126 and a cap layer 128. The deep n-well region isdisposed in the p-type substrate 100. The stacked gate structure 106 ispositioned on the p-type substrate 100, while the source region 108 andthe drain region 110 are configured in the p-type substrate beside twosides of the stacked gate structure 106. The spacer 112 is disposed onthe sidewall of the stacked gate structure 106. The p-type doped region104 is configured in the deep n-well 102 and is extended from the drainregion 110 to the underneath of the stacked gate structure 106. Theinterlayer dielectric layer 114 is positioned on the p-type substrate100. The conductive plug 116 penetrates through the interlayerdielectric layer 114 and the p-type substrate 100 to short the drainregion 110 with the p-type packet doped region 104. The conductive line118 is disposed on the interlayer dielectric layer 114 and iselectrically connected with the conductive plug 116.

With the continuous miniaturization of semiconductor devices as thelevel of integration of integrated circuits increases, the dimension ofmemory cells must also reduces in order to increase the level ofintegration. According to the stacked gate flash memory cell in FIG. 1,reducing the dimension of a memory cell can be accomplished by reducingthe gate length of the memory cell. However, when the gate length isbeing reduced, the channel length under the tunnel oxide layer isreduced correspondingly. Thus, an abnormal punch through between thesource region and the drain region easily occurs, which greatly affectthe electrical performance of the memory cell, Moreover, two neighboringmemory cells may interfere with each other to slow down the operatingspeed of the device. Consequently the effect of the device is affected.Apart from the above-mentioned deficiencies, the reduction of thedimension of the flash memory is limited by the critical dimension ofthe photolithography process applied in the fabrication of the flashmemory.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a non-volatile memory deviceand a fabrication method and an operating method thereof wherein thememory cell is formed inside a trench to reduce the dimension of thememory cell and to increase the level of integration.

The present invention also provides a non-volatile memory device and afabrication method and an operating method thereof, wherein the processmargin is increased, while the steps, the cost and the time of themanufacturing process are reduced.

The present invention provides a non-volatile memory device thatincludes a substrate, a first conductive type first well region, asecond conductive type second well region, a pair of control gates, twocomposite dielectric layers, a source region and a pair of drainregions. The first conductive type first well region is disposed in thesubstrate. The second conductive type second well region is disposedabove the first conductive type first well region. The first conductivetype first well region further includes a trench therein, wherein thedepth of the trench is greater than the depth of the second conductivetype second well region. A pair of control gates is disposed on the twosidewalls of the trench. The two composite dielectric layers aredisposed respectively between the pair of control gates and thesubstrate, wherein each composite dielectric layer further includes acharge storage layer. The source region is disposed between the pair ofcontrol gates in the substrate. The pair of drain regions isrespectively disposed in the second conductive type second well regionbeside both sides of the trench.

In the above non-volatile memory device, the drain regions and thesecond conductive type second well region are electrically shorted.Further, the non-volatile memory device further includes a conductiveplug that penetrates through the junction of the drain region and thesecond conductive type second well region. The source region and thedrain region are doped with n-type ions, and the second conductive typesecond well region can be a p-type well region. The substrate can be ap-type substrate. The first conductive type first well region can be adeep n-type well region. The material of the charge storage layerincludes silicon nitride or polysilicon, for example. A pair ofconductive spacers is formed, in a self-aligned manner, on the pair ofcontrol gates, wherein the top part of the control gates is protrudedabove the top surface of the trench.

According to the present invention, the control gates and the compositedielectric layers are disposed in the trench. Comparing with theconventional non-volatile memory device, the use of the surface area ofthe substrate is reduced and the integration of the device is increased.

Additionally, the channel region of the non-volatile memory device ofthe present invention is disposed in the substrate (a vertical channelregion) surrounding the peripheral of the trench. The channel length canbe accurately controlled by controlling the depth of the trench topreclude the problems encountered during the miniaturization of devices.

Further, the non-volatile memory device of the present invention employsa charge storage layer (silicon nitride) as a unit for storing charges.As a result, the work voltage required during an operation can bereduced to raise the operating speed and efficiency of the memory celland to enhance the performance of the programming/erasure operation ofthe memory device.

The reading operation of the non-volatile memory device of the presentinvention is accomplished by shorting the drain region and the secondconductive type second well region. The reading rate can thus increaseto improve the efficiency of the device.

The present invention is also directed to a non-volatile memory devicethat includes a substrate, a first conductive type first well region, aplurality of second conductive type second well regions, a plurality ofcontrol gates, a plurality of composite dielectric layers, a pluralityof source regions and a plurality of drain regions. The first conductivetype first well region is disposed in the substrate. The plurality ofsecond conductive type second well regions is disposed above the firstconductive type second well region. The first conductive type first wellregion includes a plurality of parallel-arranged trenches, and the depthof these trenches is greater than the depth of the second conductivetype second well regions. The plurality of control gates is respectivelydisposed on the sidewalls of the trench. The plurality of compositedielectric layers is respectively disposed between the control gates andthe substrate. Each composite dielectric layer is constituted with a topdielectric layer, a charge storage layer and a bottom dielectric layer.The plurality of source regions is respectively disposed in thesubstrate between two neighboring control gates in the trench. Theplurality of drain regions is respectively disposed in the secondconductive type second well region beside the two sides of the trench.

In the above non-volatile memory device, the drain regions and thesecond conductive type second well region are electrically shorted.Further, a plurality of conductive plugs is disposed in the device,wherein these conductive plugs respectively penetrate through thejunction of the drain regions and the second conductive type second wellregion. The source regions and the drain regions are doped with n-typeions, and the second conductive type second well region is a p-type wellregion. The substrate is a p-type substrate. The first conductive typefirst well region can be a deep n-type well region. The material of thecharge storage layer can be, for example, silicon nitride orpolysilicon.

According to the present invention, the control gates and the compositedielectric layers are disposed in the trench. Therefore, comparing withthe conventional non-volatile memory device, the application of thesurface area of the substrate can be reduced to raise the integration ofthe device.

Additionally, the channel region of the non-volatile memory device ofthe present invention is disposed in the substrate (a vertical channelregion) surrounding the peripheral of the trench. Therefore, the channellength can be accurately controlled by controlling the depth of thetrench to preclude the problems encountered during the miniaturizationof devices.

Further, the non-volatile memory device of the present invention employsa charge storage layer (silicon nitride) as a charge-storing unit. As aresult, the work voltage required for an operation can be reduced toimprove the operating speed and efficiency of the memory cell and toenhance the performance of the programming/erasure operation of thememory device.

The drain region and the second conductive type second well region ofthe present invention are shorted for reading the non-volatile memorydevice. Thus, the reading rate is increased to improve the efficiency ofthe device.

The present invention provides a fabrication method for a non-volatilememory device. This method includes providing a substrate and forming afirst conductive type first well region in the substrate. A secondconductive type second well region is then formed over the firstconductive type first well region. A trench is also formed in thesubstrate, wherein the depth of the trench is greater than the depth ofthe second conductive type second well region. A composite dielectriclayer is then formed on both sides of the trench. The compositedielectric layer includes a charge storage layer. A plurality ofconductive spacers is formed on the sidewall of the trench, wherein thecomposite dielectric layer is formed between the conductive spacers andthe sidewalls of the trench. Thereafter, a source region and a drainregion are formed in the substrate. The source region is formed in thesubstrate at a bottom of the trench between two neighboring conductivespacers, while the drain region is formed in the substrate above thesecond conductive type second well region.

In the above fabrication method for a non-volatile memory device, afterforming the source region and the drain region in the substrate, themethod farther includes forming an interlayer dielectric layer in thesubstrate to cover the substrate, the trench and the conductive spacers.An opening that at least exposes the drain region is formed in theinterlayer dielectric layer. Thereafter, a conductive plug is formed byfilling the opening with a conductive material. Forming the opening thatat least exposes the drain region includes removing a portion of thesubstrate such that the opening extends to the junction of the drainregion and the second conductive type second well region.

In the above fabrication method for a non-volatile memory device, beforethe step of forming the conductive spacers on the sidewalls of thetrench, a conductive layer is first formed on the substrate, followed byperforming an anisotropic etching process to remove a portion of theconductive layer. Further, a portion of the composite dielectric layeris concurrently removed. The material of the charge storage layerincludes silicon nitride and polysilicon.

The conductive spacers (control gate) of the present invention is formedby a self-alignment method without the application of thephotolithography techniques. Not only the process margin is increased,the manufacturing cost and time are reduced.

The conductive spacers (control gate) and the composite dielectric layerof the present invention are formed in the trench. Comparing with theconventional nonvolatile memory device, the use of the surface area ofthe substrate is reduced. As a result, the level of integration isincreased. Moreover, the present invention employs the charge storagelayer (silicon nitride) as the charge storage unit. Therefore, theprocess for defining the floating gate when a floating gate (dopedpolysilicon) is used as a charge-storing unit can be omitted.Accordingly, the fabrication process of the present invention is simplerand the level of integration of the non-volatile memory device can beincreased.

The present invention further provides an operating method for anon-volatile memory device, and the method includes applying a firstvoltage to the control gate, applying a second voltage to the drainregion, applying a third voltage to the source region, and using thechannel F-N tunneling effect to program the memory cell.

In the above operating method of a non-volatile memory device, the firstvoltage is about −10 volts, the second voltage is about 6 volts and thethird voltage is about 6 volts.

In the above operating method of a non-volatile memory device, during areading operation, a fourth voltage is applied to the control gate, afifth voltage is applied to the source region and a sixth voltage isapplied to the drain region to read the memory cell.

In the above operating method of a non-volatile memory device, thefourth voltage is about 3.3 volts, the fifth voltage is about 1.65 voltsand a sixth voltage is about 0 volt.

In the above operating method of a non-volatile memory device, during anerasure operation, a seventh voltage is applied to the control gate, adrain region is set at floating, an eighth voltage is applied to thesource region, and a ninth voltage is applied to the substrate to erasethe memory cell using the channel F-N tunneling effect.

In the above operating method of a non-volatile memory device, theseventh voltage is about 10 volts, the eighth voltage is about −6 volts,and the ninth voltage is about −6 volts.

The programming and the erasure operations of a non-volatile memorydevice of the present invention applies the channel F-N tunnelingeffect. Therefore, the consumption of electric current is small and thepower dissipation of the entire wafer is effectively lowered. Moreover,during the programming operation, using channel F-N tunneling with ahigher electron injection efficiency can lower the memory current andincrease the operating speed.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic, cross-sectional view of a portion of aconventional stacked gate type of flash memory cell structure.

FIG. 2 is a schematic, cross-sectional view of a non-volatile memorydevice structure according to an embodiment of the present invention.

FIGS. 3A through 3F are schematic cross-sectional views showing thesteps for fabricating a flash memory device according to an embodimentof the present invention.

FIG. 4 is a simplified circuit diagram of a non-volatile memory deviceaccording to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

FIG. 2 is a schematic, cross-sectional view of a non-volatile memorydevice structure. The following discussion will be based on abi-directional tunneling program/erase NOR (BiNOR) array of non-volatilememory for illustration.

Referring to FIG. 2, the non-volatile memory device of the presentinvention is formed with a p-type substrate 200, a deep n-type wellregion 202, a p-type well region 204, a control gate 206, a sourceregion 208, a drain region 210, a composite dielectric layer 212, aninterlayer dielectric layer 214, a conductive plug 216, a conductiveline 218 (bit line).

The p-type substrate 200 includes a plurality of parallel arrangedtrenches 220. The deep n-type well 202 is positioned, for example, inthe p-type substrate 200. The p-type well region 204 is disposed, forexample, above the n-type well region 202, and is arranged between everytwo neighboring trenches 220 in the substrate 200. Thus, the p-type well204 is an isolated well. The junction of the deep n-type well region 202and the p-type well region 204 is higher than the bottom of the trench220. The depth of the trench 220 is greater than the depth of the p-typewell region 204.

The control gate 206 is disposed, for example, on the two sidewalls ofthe trench 220, wherein the top of the control gate 206 is protrudedfrom the surface of the substrate 200. The composite dielectric layer212 is disposed, for example, between the control gate 206 and thesubstrate 200. The composite dielectric layer 212 includes a topdielectric layer 212 a, a charge storage layer 212 b and a bottomdielectric layer 212 c, for example. The material of the top dielectriclayer 212 a includes, but not limited to, silicon oxide. The material ofthe charge storage layer 212 b is, for example, silicon nitride. Thematerial of the bottom dielectric layer 212 c includes, but not limitedto, silicon oxide. The material of the charge storage layer 212 b can beother material that includes the charge storage property, such aspolysilicon, silicon oxynitride, etc.

The source region 208 is disposed, for example, beside one side of thecontrol gate at the bottom of the trench 220. In other words, the sourceregion 208 is disposed in the substrate 200 between two neighboringcontrol gates 206 in the trench 220. The source regions 208 areconnected together through the n-type well region 202 to form the commonsource line. The drain region 210 is disposed, for example, besideanother side of the control gate 206 in the substrate 200. In otherwords, the drain region 210 is disposed beside the two sides of thetrench 220 in the p-type well region 204.

The interlayer dielectric layer 214 is disposed on the p-type substrate200. The conductive plug 216 penetrates through the interlayerdielectric layer 214 and the p-type substrate 200, shorting the drainregion 210 and the p-type well region 204. The conductive line 218 isdisposed above the interlayer dielectric layer 214 and is electricallyconnected with the conductive plug 216.

The control gate 206 and the composite dielectric layer 212 of thepresent invention are disposed in the trench 220. Therefore, comparingwith the conventional non-volatile memory device, the use of thesubstrate surface area can be reduced to increase the level ofintegration of the device.

Further, the channel region (vertical type of channel region 222) of thenon-volatile memory device of the present invention is disposedsurrounding the peripheral of the trench in the substrate. Thus, thechannel length can be accurately controlled by controlling the depth ofthe trench to avoid problems generated during the miniaturization ofdevices.

Further, the non-volatile memory device of the present inventionutilizes the charge storage layer (silicon nitride) as thecharge-storing unit. Not only the work voltage required for operationcan be lower, the operating speed and efficiency of the memory cell canbe increased to enhance the performance of the programming/erasureoperation of the memory device.

Moreover, the reading operation of the non-volatile memory device isaccomplished by shorting the p-type well region 204 and the drain region210. Accordingly, the reading rate is increased and the performance ofthe device is enhanced.

The fabrication method for a non-volatile memory device according to anembodiment of the invention is discussed hereinafter. FIGS. 3A through3F are schematic cross-sectional views showing the steps for fabricatinga flash memory device according to an embodiment of the presentinvention. The following discussion will be based on a BiNOR array ofnon-volatile memory for illustration.

Referring to FIG. 3A, a p-type substrate 300 is provided. The p-typesubstrate 300 is already completed with device isolation structures (notshown). The device isolation structures are arranged in a strip patternto define the active region. The method used in forming the deviceisolation structures includes, local oxidation (LOCOS) or shallow trenchisolation (STI). Thereafter, a deep n-type well region 302 is formed inthe p-type substrate 300, followed by forming a p-type well region 304above the n-type well region 302. The deep n-type well region 302 andthe p-type well region 304 are formed by ion implantation, for example.

Referring to FIG. 3B, a pad oxide layer 306 and a mask layer 308 aresequentially formed on the surface of the substrate 300.Photolithography and etching processes are performed to pattern the masklayer 308 and the pad oxide layer 306 to form an opening (not shown inFigure) that exposes the substrate 300. The pad oxide layer 306 includessilicon oxide, for example, and is formed by methods such as thermaloxidation. The material of the mask layer 308 is silicon nitride, forexample. Forming the mask layer 308 includes, but not limit to,performing chemical vapor deposition (CVD).

Using the mask layer 308 as a mask, an etching process is performed toform a trench 310 in the substrate 300. The depth of the trench 310 isgreater than the depth of the p-type well region 304. Etching the trench310 in the substrate 300 includes performing dry etching, such as,reactive ion etching.

Continuing to FIG. 3C, a composite dielectric layer 312 is formed on thesubstrate 300. The composite dielectric layer 312 includes a topdielectric layer 312 a, a charge storage layer 312 b and a bottomdielectric layer 312 c. The material of the top dielectric layer 312 aincludes silicon oxide, for example. The material of the charge storagelayer 312 b includes silicon nitride, for example. The material of thebottom dielectric layer 312 c includes silicon oxide, for example. Thecomposite dielectric layer 212 is formed by, for example, using athermal oxidation method to form the bottom dielectric layer 312 c,followed by using a chemical vapor deposition method to form the chargestorage layer 312 b and the top dielectric layer 312 a.

Thereafter, as shown in FIG. 3D, a plurality of conductive spacers 314is respectively formed on the sidewalls of the trench 310, wherein theconductive spacer 314 serve as the control gates. The conductive spacers314 are formed by, for example, forming a conductive layer, followed byperforming an anisotropic etching process to remove a portion of theconductive layer. The material of the conductive layer (conductivespacer 314) includes doped polysilicon, which is formed by, for example,performing a chemical vapor deposition process to form an undopedpolysilicon layer, followed by conducting an ion implantation process.The conductive layer can also form by an in-situ doping during achemical vapor deposition process. In the step of forming the conductivespacer 314, portions of the composite dielectric layer 312 on thesurface of the mask layer 308 and between the conductive spacers 314 areremoved, leaving behind the composite dielectric layer 312 between theconducive spacers 314 and the sidewall of the trench.

As shown in FIG. 3E, after removing the mask layer 308 and the pad oxidelayer 306, an ion implantation process is performed to form a sourceregion 316 and a drain region 318 in the substrate 300 using theconductive spacers 314 as a mask. The source region 316 is disposed inthe substrate 300 between the conductive spacers 314 at the bottom ofthe trench 310. The drain region 318 is disposed above the p-type wellregion 304 in the substrate 300.

Referring to FIG. 3F, an interlayer dielectric layer 320 is formed onthe substrate 320. The interlayer dielectric layer 320 is formed withborophosphosilicate glass (BPSG) or phosphosilicate glass (PSG). Theinterlayer dielectric layer 320 is formed by, for example, chemicalvapor deposition. Thereafter, a planarization process (for example,etching-back, chemical mechanical polishing) is performed to planarizethe surface of the interlayer dielectric layer 320. A conductive plug322 is then formed in the interlayer dielectric layer 320. Theconductive plug 322 is formed with, for example, tungsten. Theconductive plug 322 is formed by, forming an opening (not shown) thatexposes the drain region 318 in the interlayer dielectric layer 320,followed by filling the opening with a conductive material. Further,during the step of forming the opening that exposes the drain region inthe interlayer dielectric layer 320, a portion of the substrate at thedrain region 318 is removed such that the opening is formed penetratingthrough the junction of the drain region 318 and the p-type well region304. In other words, the conductive plug 322 penetrates through thejunction of the drain region 318 and the p-type well region 304 toelectrically short the drain region 318 and the p-type well region 304.A conductive line 324 is then formed on the interlayer dielectric layer320 to electrically connect with the conductive plug 322. The conductiveline 324 is formed by, for example, forming a conductive layer (notshown) on the substrate 300, followed by performing photolithography andetching processes to form the strip-shape pattern conductive line 324.The fabrication of a flash memory device is subsequently formed byresorting to the conventional techniques and will not be reiteratedherein.

The formation the conductive spacer 314 (control gate) can be formed bya self-aligned method without the application of the photolithographytechniques. Not only the process margin can be increased, themanufacturing cost and time can be increased.

Moreover, the conductive spacer 314 (control gate) and the compositedielectric layer 312 of the present invention are formed in the trench310. Comparing with the conventional non-volatile memory device, theusage of the substrate surface can be reduced to increase the level ofintegration. Moreover, the present invention applies a charge storagelayer (silicon nitride) as a charge-storing unit. Therefore, the stepfor defining a floating gate when a floating gate is used for acharge-storing unit can be omitted, Not only the manufacturing processof this invention is simpler, the level of integration of thenon-volatile memory device is increased.

Although the disclosure herein refers to certain illustrated embodimentsof a n-channel non-volatile flash memory device, it is to be understoodthat these embodiments can also be presented by way of an p-channelnon-volatile memory device.

FIG. 4 is a simplified circuit diagram of a non-volatile memory deviceaccording to an embodiment of the present invention. The disclosureherein refers to an eight-memory-cell array of a bi-directionaltunneling program/erase NOR (BiNOR) type for illustrating the operationsof the memory array of the present invention.

Referring to FIG. 4, the memory array includes 8 memory cells Q11˜Q24,the word line WL1˜WL4, the bit line BL1˜BL2, and the common source lineSL.

Each memory cell Q11˜Q24 has a structure as shown in FIG. 2. Twoneighboring memory cells share a drain region. The two memory cells thatdo not share a drain region share a source region.

The bit lines BL1˜BL2 are respectively connected to the drain regions ofthe same row of memory cells. For example, the bit line BL1 connects thedrain regions of the memory cells Q11˜Q14, while the bit line BL2connects the drain regions of the memory cells Q21˜Q24.

The word lines WL1˜WL4 are respectively connected to control gates ofthe memory cells of the same column. For example, the word line WL1connects the control gates of the memory cells Q11˜Q21, the word lineWL2 connects the control gates of the memory cells Q12˜Q22, the wordline WL3 connects the control gates of the memory cells Q13˜Q23, and theword line WL4 connects the control gates of the memory cells Q14˜Q24.The source regions of all memory cells are connected together throughthe deep n-type well region to form a common source line SL.

Concurrently referring to FIG. 4 and Table 1, FIG. 4 and Table 1illustrate the operation which include the programming, the erasure andthe reading operations of the non-volatile memory device of the presentinvention.

TABLE 1 Programming Erasure Reading Selected word line Vgp Vge Vgr WL2(−10 V) (10 V) (3.3 V) Non-selected word line Vg Vge 0 WL1, WL3, WL4 (−2V) (10 V) Selected bit line Vdp Floating 0 BL2 (6 V) Non-selected bitline 0 Floating Floating BL1 Source line, SL Vsp Vse Vsr (6 V) (−6 V)(1.65 V) Substrate 0 Vbe 0 (−6 V)

Referring to FIG. 4, when the memory cell Q22 is performing aprogramming operation, a voltage Vgp, for example, −10 volts is appliedto the selected word line WL2. A bias voltage Vdp, for example, −2volts, is applied to other non-selected word lines WL1, WL3, WL4. Avoltage Vdp, for example, 6 volts, is applied the selected bit line BL2,while a voltage of 0 volt is applied to the non-selected bit line BL1. Abias voltage Vsp, for example, 6 volts, is applied to the source line.Under these types of bias voltages, the channel F-N tunneling effect canbe used to inject electrons into the charge storage layer to program thememory cell Q22.

During the above-mentioned programming operation, the memory cell Q12that share the common word line WL2 with the memory cell Q22 is notprogrammed. This is due to the fact that a voltage of 0 volt is appliedto the bit line and the channel F-N tunneling effect will not beinvoked. Accordingly, the memory cell Q12 is not programmed.

A voltage of −2 volts applied to the non-selected word lines WL1, WL3,WL4 is not sufficient to invoke the channel F-N tunneling effect. Thememory cells Q11˜Q21, Q13˜Q23, Q14˜Q24 that are connected by thenon-selected word lines WL1, WL3, WL4 are not programmed.

Although the above-mentioned programming operation is performed on asingle memory cell in the memory device array, the programming of thenon-volatile memory device of the present invention can be conducted inbyte or page by controlling the various word lines, source lines and bitlines.

To read the information in memory cell Q22, a bias voltage of Vgr, forexample, about 3.3 volts, is applied to the selected word line WL2,while 0 volt is applied to other non-selected word lines WL1, WL3, WL4.The selected bit line BL2 is applied with about 0 volt, while thenon-selected bit line BL1 is set floating. The source line SL issupplied with a bias voltage of about 1.65 volts, for example. Since thechannel of the memory cell having charges being stored in the chargestorage layer is closed and there is no current flow and the channel ofmemory cell having no charges being stored in the charge storage layeris opened and the current flow is large, the digital information storedin the memory cell being [1] or [0] can be determined by the opening orclosing/the amount of current flow at the channel of the memory cell.

Although the above-mentioned reading operation is performed on a singlememory cell in the memory device array, the reading of the non-volatilememory device of the present invention can be conducted in terms ofbyte, sector or block by controlling the various word lines, sourcelines and bit lines.

The erasure method of the non-volatile memory device of the presentinvention is disclosed hereinafter. As shown in Table 1, the erasuremethod of the present invention is directed to, as an example, theentire non-volatile memory device.

As the memory cell is performing the erasure operation, a bias voltageVge, for example, about 10 volts, is applied to all the word linesWL1˜WL4, while the bit lines are set floating. A bias voltage Vse, forexample, about −6 volts, is applied to the source line SL. A biasvoltage Vbe, for example, about −6 volts, is applied to the substrate.Since the voltage applied between the control gate and the substrate issufficient to establish a large electric field between the control gateand the substrate, the channel F-N tunneling effect can be used to expelthe charges from the charge storage layer and to remove the charges byinjecting the charges into the substrate.

Although the above-mentioned erasure operation is performed on theentire memory device array, the erasure of the non-volatile memorydevice of the present invention can be conducted in sector or block bycontrolling the various word lines, source lines and bit lines.

Since the programming and the erasure operations of the non-volatilememory device utilize the channel F-N tunneling effect, the currentconsumption is small to effectively lower the power dissipation of theentire memory array. Moreover, during the programming operation, usingchannel F-N tunneling with a higher electron injection efficiency canlower the memory current and to increase the operating speed.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A method for fabricating a non-volatile flash memory device, themethod comprising: providing a substrate; forming a first conductivetype first well region in the substrate; forming a second conductivetype second well region above the first conductive type first wellregion; forming a trench in the substrate, wherein a depth of the trenchis greater than a depth of the second conductive type second wellregion; forming a composite dielectric layer at both sides of thetrench, wherein the composite dielectric layer comprises a chargestorage layer; forming a pair of conductive spacers on sidewalls of thetrench, wherein the composite dielectric layer is disposed between theconductive spacers and the sidewall of the trench; and forming a sourceregion and a pair of drain regions in the substrate, wherein the sourceregion is formed in the substrate between two of the neighboringconductive spacers, and the drain regions are formed on two sides of thetrench in the second conductive type second well region.
 2. The methodof claim 1, wherein after the step of forming the source region and thedrain regions in the substrate, the method further comprises: forming aninterlayer dielectric layer on the substrate to cover the substrate, thetrench and the conductive spacers; forming an opening in the interlayerdielectric layer, wherein the opening at least exposes the drain region;and filling a conductive material into the opening to form a conductiveplug.
 3. The method of claim 2, wherein in the step of forming theopening in the interlayer dielectric layer, the opening further exposesa part of the second conductive type second well region.
 4. The methodof claim 1, wherein the step of forming the pair of conductive spacerson the sidewall of the trench further comprises: forming a conductivelayer on the substrate; and performing an anisotropic etching process toremove a portion of the conductive layer.
 5. The method of claim 4,wherein the step of performing the anisotropic etching process to removethe portion of the conductive layer further comprises removing a portionof the composite dielectric layer.
 6. The method of claim 1, wherein amaterial constituting the charge storage layer comprises siliconnitride.
 7. The method of claim 1, wherein a material constituting thecharge storage layer comprises polysilicon.